It is generally known to provide for a window covering venetian blind with the slats that are raised and lowered by a pair of lift cords. Such known window coverings typically include lift cords that are secured to a bottom rail and extend upward through the slats into a head rail. The lift cords are guided within the head rail and exit through a cord lock and hang outside of the window covering. In order to raise or lower the window covering, the lift cords are manipulated to first release the cord lock. Similarly, once the window covering has been raised or lowered the cord lock is manipulated again to lock the cords in place. However, such an arrangement may present a safety concern to small children and pets.
Blinds and shades in which the lift cords are contained within the bottom rail, window covering and head rail are referred to as “cordless” blinds and shades because no portion of the lift cords is external to the blind or shade. Cordless blinds have been gaining popularity and are employed in a wide variety of blinds and shades such as venetian blinds, cellular blinds, pleated shades, and wood blinds.
One way to provide a “cordless” blind is to “balance” the window blind system. In a “balanced” cordless blind, the spring force of the spring motor is balanced by the combined weight of the bottom rail (and any accumulated window covering) and friction, sometimes misidentified in the field as inertia. In such balanced systems the friction is greater than the difference between the spring force and the combined weight of the bottom rail and accumulated window covering when the bottom rail is at any location between a fully extended position and a fully retracted position. However, such known cordless blinds have several disadvantages for a mass-merchandise avenue of distribution, including, for example, the need for friction systems that are costly to assemble and manufacture. Also, these cordless blinds do not lend themselves to size-in-store adjustment.
Another way to provide a “cordless” blind is to include a brake that is configured to clamp onto one or more of the lift cords or engages the spring motor. One such known blind is shown in U.S. Pat. No. 6,029,734, and shows a venetian blind having a spring retrieving unit and spindle in a head rail, and a cord brake mechanism in a bottom rail. However, because the cord brake mechanism is located in the bottom rail while the spring motor is in the head rail and the lift cords connect the bottom rail to the head rail, it is only useful to prevent the bottom rail from free falling. As such, the spring retrieving unit must be weak so that the bottom rail does not creep upward. Also, opening of blind requires the user to exert effort to lift bottom rail and patience to wait for the weak spring retrieving units to wind up the slack cords.
Accordingly, it would be advantageous to provide a window covering with a strong spring motor that is configured to bias the bottom rail upward and capable of raising bottom rail absent a brake. It would also be advantageous to provide a cordless window covering with a cord brake that prevents the bottom rail from moving up or down. Additionally, it would be advantageous to provide a cordless window covering that may be custom sized at the point of purchase.
A brake system that overcomes the disadvantages of the more complex and cumbersome systems of the prior art would represent a significant advance in this art.